Electrochemical oxidation of organometallic complexes. Carbene and Lewis base complexes of chromium, molybdenum, and tungsten carbonyls

Tha oxidative one-electron transfer reactions of a wide variety of Group VI metal carbonyl derivatives have been detected by voltammetry. The compounds studied are of the type M(CO)6 –nLn or M(CO)6 – 2n(LL)n(M = Cr, Mo, W; L = monodentate Lewis base, n= 1 or 2; LL = bidentate Lewis base, n= 1 or 2) and carbene complexes of the type M(CO)5C(X)Y. The value of the potential, E½, is influenced by each of the variables M, L(or LL), n, X, and Y. The order of E½-values follows closely the apparent π-acceptor/σ-donor ratio of the ligand, but comparison with the results of molecular orbital calculations suggests that the influence of L (or of {C(X)Y}) upon the redox orbital is indirect. Steric effects are shown to influence the value of E½, especially where bidentate ligands are present. The oxidation potentials are related to synthetic chemistry in these systems.